In the photographic art color images are formed by the exposure of a silver halide light sensitive element containing organic dye forming couplers followed by processing in aqueous developer solutions containing an aromatic primary amine color developing agent. The resultant dyes formed are yellow, magenta, or cyan and result in the formation of a color image in the photographic element.
There are several heterocyclic organic materials known to form magenta or cyan images such as pyrazolones, pyrazolobenzimidazoles, pyrazolotriazoles, indazoles, imidazopyrazoles, and imidazoimidazoles. The heterocyclic nitrogen compound pyrazolotriazole is extensively used in modem photographic color materials. Bailey's original patent BP 1,252,418 (1971) describes the pyrazolo[5,1-c]-1,2,4-triazole heterocyclic nitrogen compound for use in photographic elements.
Color forming image dyes in photographic elements must have desirable hues and good stability with little or no fading or discoloration under storage in the dark or when exposed to light. The couplers which form these dyes should have good coupling efficiency and lead to dye images with high contrast and high density in areas of maximum exposure and low density in areas of minimum exposure.
It is well recognized by those skilled in the art that modifications of the structure of the substituents on the pyrazolo[5,1-c]-1,2,4-triazole heterocycle can have important effects on the dyes formed from these couplers, including improvements in dye image stability, etc. Thus, the researcher skilled in the art of photographic couplers is always seeking new substituents on the pyrazolo[5,1-c]-1,2,4-triazole heterocycle with an aim to discover ever better image dye properties. In recent years many patents have been issued on variations of the 3-alkyl substituted pyrazolo[5,1-c]-1,2,4-triazole couplers. These couplers have the required hue, contrast, and efficiency properties necessary to produce superior image dyes in modem photographic materials. Nevertheless, new substituent research continues.
In Bailey's original patent BP 1,252,418 (1971) a wide range of substituents are described as useful in varying the hue and properties of pyrazolo[5,1-c]-1,2,4-triazole image dyes. In particular, Bailey describes the 3-heterocyclic substituents pyridine and thiophene. Recently, Iizuka et.al. JP 10161284 (1998) have described the 5 member ring .alpha.-substituted pyrrole, imidazole, pyrazole, thiophene, furan, thiazole, oxazole, and triazole heterocycles as particular couplers with improved performance compared to 3-alkyl substituted pyrazolo[5,1-c],-1,2,4-triazole couplers. Iizuki et. al. in JP 10133342 (1998) also describe the 6 member ring a substituted pyridine, pyridazine, pyrimidine, pyrazine, and benzoxazole heterocycles with improved performance compared to 3-alkyl substituted pyrazolo[5,1-c]-1,2,4-triazole couplers. These couplers may generically be described by structure A below in which Z represents the elements of C, N, O, and S required to form 5 and 6 member rings containing a R substituent in the .alpha. position of the ring adjacent to the carbon bonding the heterocycle to the 3 position of the pyrazolo[5,1-c]-1,2,4-triazole ring. ##STR2##
It should be particularly noted in this structure that the heterocycle bonded to the 3 position of the pyrazolo[5,1-c]-1,2,4-triazole ring is bonded to a carbon atom of the heterocyclic substituent. This is a common feature of heterocyclic substituted pyrazolo[5,1-c]-1,2,4-triazole couplers dating back to the originally disclosed pyridine and thiophene substituents of Bailey BP 1,252,418 (1971).
The Chemical Abstracts registry file reveals that no pyrazolo[5,1-c]-1,2,4-triazole couplers have been reported in which the 3 position of the pyrazolo[5,1-c]-1,2,4-triazole ring is bonded to a nitrogen atom of the heterocyclic substituent. Broad disclosures of pyrazole compounds bearing a wide variety of substituents including heterocycles such as pyrazolyl groups have been mentioned (WO 97/35551) but there has been no specific disclosure with a pyrazolo[5,1-c]-1,2,4-triazole, and there has been disclosed no method of synthesis of such compounds. The synthesis of such novel pyrazolo[5,1 -c]-1,2,4-triazole couplers is unknown to those skilled in the art. The properties of such unknown pyrazolo[5,1-c]-1,2,4-triazole couplers would be of very high interest to the skilled photographic coupler researcher.
We now wish to report the simple synthesis of these novel pyrazolo[5,1 -c]-1,2,4-triazole couplers, the formation of novel azomethine dyes therefrom, and the improved light stability demonstrated by these dyes in comparison to dyes from 3-alkyl substituted pyrazolo[5,1-c]-1,2,4-triazole couplers in a photographic element.